The present invention relates to a liquid crystal display device having color filters.
As liquid crystal display devices, a transmission type display device that displays using light from a backlight and a reflection type display device that displays using external light such as natural light or indoor illumination light are known. In the reflection type liquid crystal display device, a reflecting member is placed on the rear side to reflect external light incident from the front side.
Liquid crystal display devices also include devices of various schemes such as active matrix display devices and simple matrix display devices. For example, in a liquid crystal display device of the active matrix scheme, a matrix of pixel electrodes and a plurality of active elements respectively connected to the pixel electrodes are formed on the inner surface of one of a pair of substrates opposing each other through a liquid crystal layer. A counter electrode is formed on the inner surface of the other substrate, and pixel areas are formed by the portions where the counter electrode opposes the respective pixel electrodes.
In a liquid crystal display device for displaying a color image, color filters are arranged on the inner surface of one of a pair of substrates in correspondence with the respective pixel areas.
In a conventional liquid crystal display device having color filters, however, when light transmitted through a given pixel area is incident on the corresponding color filter, light having wavelengths other than a specific wavelength range is absorbed by the color filter, and only the light in the specific wavelength range is transmitted, thereby displaying with the transmitted light colored with the color of the color filter. For this reason, the intensity of the colored exit light becomes much lower than that of the incident light, and a bright display cannot be obtained.
To increase the brightness, the red, green, and blue color filters may be made thinner to reduce the amount of light absorbed by the color filters so as to increase the light transmittance. As a result, the screen may become bright. If, however, the color filters are made thinner in this manner, the transmittance in the absorption wavelength range of each of colored light beams, i.e., red, green, and blur light beams, increases, and the color balance between light beams of the respective colors deteriorates, as shown in FIG. 28. As a result, a good white display cannot be obtained.
FIG. 28 shows changes in spectral transmittance with reductions in the thicknesses of color filters. As shown in FIG. 28, according to the spectral distribution (solid line) of red light transmitted through a red filter, the light transmittance on the short wavelength side as the absorption wavelength range of the red filter is high, as indicated by the dashed line. According to the spectral distributions (solid lines) of green light and blue light which are respectively transmitted through the green and blue filters, the half widths of the light transmittances tend to increase. As a result, the spectral transmittance of the color light mixture exhibits a high peak of transmittance at a wavelength in the neighborhood of 500 nm. In a liquid crystal display device having thin color filters, therefore, the transmittance in the absorption wavelength range of each of colored light beams, i.e., red, green, and blur light beams, increases, and hence the purity of each color deteriorates. In addition, since the color balance between light beams of the respective colors is poor, the display color obtained by additive color mixture becomes close to cyan (bluish green).
As described above, the screen of the conventional reflection type color liquid crystal display device is dark because of light absorption in the color filters. Even if the amount of light absorbed by each color filter is decreased, the color balance suffers. As a result, a satisfactory white display cannot be obtained.